ROCR is an Oscillating Climbing Robot

X’s indicate wall attachment    

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Introduction to ROCR

We present a novel climbing robot, with a recursive name, ROCR: ROCR is an Oscillating Climbing Robot. ROCR is a pendular two-link, serial chain robot that utilizes alternating handholds and an actuated tail to propel itself upward in a climbing style based on observation of human climbers and brachiating gibbons. ROCR’s bio-inspired oscillating climbing strategy is efficient, requiring a minimum of input energy in order to climb vertical walls. This robot is intended for autonomous surveillance, inspection, and maintenance on sheer vertical surfaces. Several locomotion gait strategies for ROCR (already investigated in simulation) have been implemented in hardware experiments (see movie or YouTube movie links below).

Full view of V7 ROCR body on the carpet wall:

Closeup of V7 ROCR body showing PCB and gear from front:

Detailed view of V7 ROCR body showing hook engaging wall, shear transfer spacer, and final gear system in the new body:

Detailed view of V7 ROCR body from the wall side, showing final gear system and the adjustable gear spacing in the new body:

!!!Physical Design of ROCR ----------- ROCR is a T-shaped, pendular two-link, serial chain robot with a pivoting tail attached to the bottom of the T (as shown in Fig. 1) and two gripping mechanisms (hands, as shown in Figs. 1 & 2), one at each end of the T’s crossbar. The top of the T is 30.5 cm across, the swinging portion of the tail is 45.7 cm long and the joint location of the tail is adjustable such that it can be moved from 5–20 cm below the centerline between the robot’s gripping mechanisms. ROCR’s bio-inspired oscillating climbing strategy is the key to its efficient climbing gaits. ROCR alternately grips the wall with one hand at a time and swings its tail, causing a center of gravity shift that raises its free hand, which then grips the climbing surface as portrayed in Fig. 4. The hands swap gripping duties and ROCR swings its tail in the opposite direction. As ROCR’s tail oscillates from side to side, the resultant center of gravity changes, which, coordinated with gripping activity, will drive the robot up a vertical surface. A first generation ROCR prototype is shown in Fig.3.

(a) (b)
Fig. 1. (a) Image of Climbing Robot, ROCR. (b) Image of upper body, showing the tail gear, electronics, and claws.


Fig. 2. Image showing claw attachment to the Climbing Wall

Fig 1. Solid model screen capture of ROCR, as designed, is shown with components labeled Fig 2. ROCR will initially use magnetic gripping mechanisms, these are shown in section view above. Note magnetic piston, topped by encoder, slides within bushing which rotates within bearings. The bushing is capped with a urethane friction ring which works to prevent the piston from sliding as body pivots about grip. Fig 3. ROCR, in a preliminary assembly, is shown with components labelled

Bio-Inspired Climbing Strategy

Proficient human climbers take advantage of both subtle and dramatic mass shifting to gain elevation with minimal physical effort. A simple lateral body movement prior to changing handholds often enables a human climber to reach higher with less pull-up effort. Human climbers often engage in dramatic mass shifting in preparation for highly dynamic climbing motions, essentially winding-up and then releasing their potential energy (PE) into a large vertical gain.

Brachiation is most notably employed by gibbons when they swing from one handhold to the next in a dynamic pattern of gripping and swinging. Brachiative motion strings together a sequence of pendular paths with coordinated grip changes to achieve lateral motion. In this method of lateral swinging motion, very little input energy is required to maintain physical progress. ROCR turns standard gibbon brachiation vertical, combining it with human style mass shifting into a tail-swinging body-oscillating scansorial climbing strategy.

By mimicking climbing strategies employed by human climbers and animals, a simple, energy efficient climbing strategy has been developed. ROCR uses precise mass shifts, affected by a carefully controlled tail motion, to raise one hand at a time. Combining and integrating these behaviors enables ROCR to climb efficiently with a minimum of mass and moving parts.

Initial Climbing Gaits

The pendular two-link design of ROCR dictates the method by which the robot will climb; however, many climbing gaits are possible. Different gaits engage and disengage the wall (or holds) with their gripping mechanisms (or hands) at different times during the oscillatory swinging of the tail (or shifting of their mass). Two preliminary climbing gaits were identified for ROCR. These gaits, shown in Fig 3, are a function of the tail motion frequency and are referred to as Quasi-Static and Dynamic gaits, for slow and fast tail motions, respectively. A movie showing the slower Quasi-static and faster/more efficient dynamic gait is shown in Fig. 4 below.

Fig 3. Example climbing gaits for ROCR. (a) Quasi-static mass shifting, equilibrium-based gait. (b) Oscillating dynamic gait achieves higher efficiency as the system approaches resonance. Robot motions resulting from a half period of tail motion is shown in (a) and (b). An engaged unidirectional gripper is shown as a yellow triangle. Arrows indicate tail motion relative to robot body and body rotation about an engaged gripping mechanism.

As shown in Fig 1. above, 3 preliminary climbing gait strategies have been developed for ROCR. The gaits are described below: Static Gait
#Both hands grip while tail swings #Tail fixed while one grip releases #Body pivots about gripping hand Simple Oscillator Gait
#One hand grips while tail swings #Body pivots about gripping hand #Gripping hands swap

Fig. 4. Movie showing ROCR climbing a carpeted wall. When ROCR's tail is driven near resonance, the robot achieves >20% climbing efficiency (defined as the ratio of work performed in the act of climbing to the electrical energy consumed by the robot). (Link to YouTube site of same movie)


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